As a therapeutic agent of diabetes, biguanide compounds having, as a main action, an inhibitory action on glucose absorption via the intestinal tract and on glucose release from the liver, sulfonylurea compounds having an accelerating action on insulin secretion as a main action, insulin and the like have been employed. However, biguanide compounds cause lactic acidosis, and sulfonylurea compounds sometimes cause serious hypoglycemia due to their strong hypoglycemic action. Therefore, a due care should be given when in use of these compounds. In recent years, there have been active researches and developments of a therapeutic agent of diabetes, which is free of these defects, with the consequence that various compounds having an insulin resistance-improving action have been found.
The insulin resistance plays an important role as a cause of non-insulin dependent diabetes mellitus (NIDDM), along with decrease in the insulin secretion. As an agent that improves insulin resistance, various thiazolidine compounds are known. Examples of such compound include 5-[4-[(6-hydroxy-2,5,7,8-tetramethylchroman-2-yl)methoxy]benzyl]-2,4-thiazolidinedione (general name: troglitazone) is described in U.S. Pat. No. 4,572,912 and EP0139421B1, 5-[[4-[2-(5-ethyl-pyridin-2-yl)ethoxy]phenyl]methyl]-2,4-thiazolidinedione (general name: pioglitazone) is described in U.S. Pat. No. 4,687,777 and EP0193256B1, and 5-[[4-[2-[N-methyl-N-(pyridin-2-yl)amino]ethoxy]phenyl]methyl]-2,4-thiazolidinedione (general name: rosiglitazone) is described in U.S. Pat. No. 5,002,953 and EP0306228B1. However, these pharmaceutical agents that improve insulin resistance may cause side effects such as hepatopathy, retention of fluid, edema, megalocardia; obesity and the like. Thus, the development of a highly safe insulin resistance improver effective for NIDDM has been desired.